Water fill systems for automatic washing machines typically include a water mixing valve having dual inlets for connection to a source of heated water and a source of cold water, to provide a mixed flow of water at a desired temperature for use in the washing machine.
As shown in FIG. 1A, in one commonly utilized form of such a mixing valve 10, a first and a second solenoid actuated diaphragm valve 12, 14 are operatively connected to a mixing valve manifold 16, which is adapted for connection to a source of hot water, a source of cold water, and to provide a mixed stream of flow from the hot and cold sources at an outlet 22 of the mixing valve 10. As show in FIGS. 1A and 1B, the manifold 16 of such mixing valves 10 typically includes a body 24 which defines the first fluid inlet 18, the second fluid inlet 20, the fluid outlet 22, a first diaphragm chamber 26 for the first control valve 12, a second diaphragm chamber for the second control valve 14, and an L-shaped outlet conduit 30 which is connected directly in fluid communication between the outlet 22 and the first and second diaphragm chambers 26, 28. By virtue of this arrangement, mixing of the fluid streams entering the mixing valve through the first and second inlets 18, 20 can occur along the entire length of the outlet conduit 30.
Manifolds 16 of the type described above, having an outlet conduit 30 providing direct fluid communication between the first and second diaphragm chambers 26, 28 and the outlet 22, have been utilized for many years, and provide very satisfactory performance where the pressure of the fluid sources attached to the first and second inlets 18, 20 are substantially equal. Generally in circumstances where both the first and second inlet 18, 20 receive fluid from the same ultimate source, such as a city water main, or a pressure tank of a well system, the pressure at the first and second inlets 18, 20 will remain substantially equal, even though the fluid stream to the first inlet 18, for example, may flow through a water heater prior to reaching the mixing valve 10.
FIG. 1C, and arrows 21 in FIG. 1D illustrate the manner in which water will flow through a prior mixing valve 10, of the type described above, when the pressure is substantially equal at the first and second inlets 18, 20.
Where the second inlet 20 is connected to receive fluid flow from a pressurized source, such as a cold water line, and the first inlet 18 is connected to receive fluid from an unpressurized, or very low pressure source, such as a solar heater or hot water tank mounted on the roof of a building, however, it is desirable to provide means within the manifold 16 to preclude having the higher fluid pressure in the second inlet overpower the diaphragm in the first valve assembly and thereby allow a backflow of fluid from the second inlet into the first pressure source through the first inlet 18, as shown by arrow 23 in FIG. 1D.